Fix: Added start script in package.json and fix localhost port in README(FIXES GAZ-27)

[kanishksingh23]

Problem
The README documented npm start and yarn start to run the application,
but the package.json had no start script defined, causing new contributors
to get an error: Missing script: "start" when trying to run the app.
Additionally, the README referenced http://localhost:3000, but Vite uses
port 5173 by default.

Solution
Added "start": "vite" to the scripts in package.json so npm start works
as documented. Updated the localhost port to 5173 to match Vite's default.

Changes
Added "start": "vite" script to package.json
Updated localhost port from 3000 to 5173 in README.md

Testing
Ran npm start successfully. Dev server started at http://localhost:5173.

[kanishksingh23]

Hello @DavidH-1 and @abhinav-1305, please review this.

[kanishksingh23]

@DavidH-1 gentle ping

[abhinav-1305]

LGTM

[kanishksingh23]

Thank you, @abhinav-1305, for the review.